It was pointed out in our forums
today while discussing Valve on Linux
that Croteam has shared today that Serious Sam 3 is running on Linux.
Croteam is the Croatian-based game development studio known for the Serious Sam series. To their Facebook page
a few hours ago they posted a screenshot of Serious Sam 3 running on Ubuntu Linux with a caption of "Serious Sam 3: BFE - running on Linux!"
No other details about the Serious Sam 3 Linux port have been shared at this time. Serious Sam 3: Before First Encounter was first released for Windows in November of 2011 and runs on the in-house Serious Engine 3.5.